Apparatus and Method For Compressing a Gas

ABSTRACT

An apparatus and method for compressing a gas is disclosed. A compressor, in particular a piston compressor, has a low pressure stage for compressing the medium from an inlet pressure to an intermediate pressure, and has a high pressure stage for compressing the medium from the intermediate pressure to a high pressure. A compensating volume with an adjustable dead volume is connected upstream of the high pressure stage.

This application claims the priority of International Application No. PCT/EP2006/006520, filed Jul. 4, 2006, and German Patent Document No. 10 2005 034 907.2, filed Jul. 26, 2005, the disclosures of which are expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a compressor, in particular a piston compressor, for compressing a gaseous medium, having a low pressure stage for compressing the medium from an inlet pressure to an intermediate pressure, and having a high pressure stage for compressing the medium from the intermediate pressure to a high pressure.

In the case of compressors for gaseous media that are embodied as piston compressors, the stage pressure ratio is determined by the cylinder dimensions. In the case of a piston compressor with two compressor stages formed by a low pressure stage and a high pressure stage, and a stage pressure ratio in the range of 17, e.g., a medium with an inlet pressure of 1 bar, can be compressed in the low pressure stage, which has a stage pressure ratio of 17, to an intermediate pressure of 17 bar, and can be compressed in the high pressure stage, which has a stage pressure ratio of 17.6, to a high pressure of 300 bar.

These types of piston compressors are designed for a specific inlet pressure, whereby the inlet pressure of the medium may only be varied within narrow limits. If a generic piston compressor that is designed for an inlet 1 bar is operated with an inlet pressure of 5 bar instead of an inlet pressure of 1 bar, an intermediate pressure of 85 bar would take effect after the low pressure stage with the stage pressure ratio of 17, which would cause the low pressure stage to overheat.

A two-stage piston compressor is known from German Patent Document No. DE 199 33 989 A1, which is suitable for different inlet pressures. In this case, separate drives are provided for the piston compressor's low pressure stage and the high pressure stage. However, this type of two-stage piston compressor with a drive for the low pressure stage and a separate drive for the high pressure stage has a construction expense that is too high.

The present invention is based on the objective of making available a compressor of the kind cited at the outset, which, with low construction expense, is suitable for different inlet pressures.

This objective is attained in accordance with the invention in that a compensating volume with an adjustable dead volume is connected upstream of the high pressure stage. With this type of compensating volume that is connected upstream of the high pressure stage and thus on the high pressure stage, it is possible in a simple manner to provide an adjustable dead volume on the high pressure stage. During the compression stroke of the low pressure stage, gaseous medium is supplied partially to the compensating volume in the process. With the subsequent supplying of the medium from the compensating volume to the high pressure stage, during the following intake stroke of the high pressure stage, the gaseous medium expands adiabatically and cools down in the process to below the intake temperature of the low pressure stage. With this type of compensating volume, it is possible to change the intake volume of the high pressure stage in a simple manner and simultaneously achieve additional cooling of the compressor. As a result, it is possible in a simple way to operate the compressor with different inlet pressures, whereby overheating of the compressor continues to be avoided.

Particular advantages are produced according to one embodiment of the invention if the dead volume formed by the compensating volume can be adjusted as a function of the inlet pressure. In this connection, it is possible to use the compensating volume to control the dead space of the high pressure stage as a function of the inlet pressure with little effort.

Special advantages are produced if the compensating volume is set at a minimum dead volume with maximum inlet pressure and with decreasing inlet pressure can be adjusted in the direction of a maximum dead volume. Thus, it is possible for the additional cooling effect to increase in a simple way with falling inlet pressure due to the compensating volume. With decreasing inlet pressure, the stage pressure ratio of the high pressure stage increases, whereby at the same time the thermal load of the compressor increases. Because of a compensating volume that forms a dead volume for the high pressure stage and is allocated to the high pressure stage, and whose cooling effect increases with a falling inlet pressure because of the expansion of the dead volume, the compressor temperature of a compressor used at different inlet temperatures can be reduced in a simple manner as a result.

The compensating volume is expediently embodied as a compensating cylinder featuring a cylinder that is displaceable in a housing. This design of the compensating volume as an adjusting cylinder makes it possible to produce an adjustable dead volume in a simple way.

According to a preferred embodiment of the invention, the cylinder is expediently provided with a first control surface as a stepped piston, which is arranged in the compensating volume and is acted upon by the intermediate pressure, and features a second control surface, which is acted upon by the inlet pressure. With this type of cylinder that is embodied as a stepped piston, it is possible in a simple manner through a corresponding selection of the sizes of the first and second control surfaces to facilitate the pressurization of the cylinder in the direction of the minimum dead volume with a maximum inlet pressure and in the direction of the maximum dead volume with decreasing inlet pressure

According to a development of the invention, the compensating volume is provided with a cooling device, whereby the medium located in the compensating volume can be cooled in a simple manner and thus the cooling effect by the compensating volume can be increased further.

According to a preferred embodiment of the invention, the cooling device is formed by cooling fins arranged on the housing, whereby a cooling device of the compensating volume can be produced at a low construction expense.

According to a preferred embodiment of the invention, the compressor features a piston that is longitudinally displaceable in a housing, which can be driven hydraulically.

The low pressure stage expediently has a first pressure chamber and a second pressure chamber, whereby the piston actuates two pressure chambers of the low pressure stage.

As a result, pulsations in the pressurized lines can be reduced by two pressure chambers with a low requirement for construction space.

According to a development of the invention, the high pressure stage has a first pressure chamber and a second pressure chamber. As a result, the piston continues to actuate two pressure chambers of the high pressure stage, whereby low pulsations can be achieved with a low requirement for construction space for the compressor.

The compressor can be cooled in a simple manner in the area of the low pressure stage and the high pressure stage if external cooling is provided on the housing.

To improve cooling, internal cooling is expediently provided on the piston.

In this case, the piston is advantageously provided with at least one longitudinal borehole, which is connected to a drive pressure chamber. As a result, internal cooling of the piston can be accomplished in a simple manner by the hydraulic pressurizing means driving the compressor.

In the case of a compressor design with a high pressure stage featuring two pressure chambers, a compensating volume is advantageously allocated to each pressure chamber of the high pressure stage.

Particular advantages are yielded with the use of a compressor for compressing hydrogen, in particular hydrogen in a hydrogen filling station.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional advantages and details of the invention are explained in greater detail on the basis of the exemplary embodiment depicted schematically in the figures. The drawings show:

FIG. 1 is a longitudinal section of an inventive compressor; and

FIG. 2 is an enlarged representation of a section of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a longitudinal section of a compressor embodied in accordance with the invention as a linear piston compressor 1.

The piston compressor 1 features a stepped piston 4 that is longitudinally displaceable in a housing borehole 2 of a housing 3, whereby a low pressure stage 5 and a high pressure stage 6 are embodied between the piston 4 and the housing borehole 2.

The high pressure stage 6 is embodied in the center region of the piston compressor 1 and features two pressure chambers 6 a, 6 b, which are embodied between a sealing element 7 arranged in the center region of the housing 3 and the piston 4. Piston sections 8 a, 8 b are arranged on the stepped piston 4 in the region of a diameter transition, whereby the pressure chambers 6 a, 6 b of the high pressure stage 6 are embodied in the region of the enlarged diameter of the piston 4. In the depicted position, whereby the piston 4 is acted upon in FIG. 1 towards the right, the left pressure chamber 6 a has a minimum displacement volume and the right pressure chamber 6 b has a maximum displacement volume.

The low pressure stage 5 is embodied on both sides of the high pressure stage 6 in the region of the reduced diameter of the piston 4 and features two pressure chambers 5 a, 5 b, which are embodied between the housing borehole 3 and the piston sections 8 a, 8 b arranged on the piston 4 in the region of the piston with the reduced diameter.

In the depicted position of the piston 4, the left pressure chamber 5 a has a maximum displacement volume and the right pressure chamber 5 b has a minimum displacement volume.

The piston compressor 1 can be driven hydraulically, whereby drive pressure chambers 9 a, 9 b that can be acted upon hydraulically are embodied on the piston 4 at the external regions adjacent to the low pressure stage 5. In the depicted position of the piston rod 4, the drive pressure chamber 9 a is being acted upon with hydraulic pressurizing means. When the drive pressure chamber 9 b is being acted upon, the piston rod 4 is acted upon correspondingly towards the left in FIG. 1.

To control the piston compressor, a low pressure suction valve 10 a, 10 b and a low-pressure pressure valve 11 a, 11 b are allocated to each of the pressure chambers 5 a, 5 b of the low pressure stage 5. A high pressure suction valve and a high-pressure pressure valve are allocated corresponding to each of the pressure chambers 6 a, 6 b of the high pressure stage 6, whereby only the high pressure suction valve 12 a and the high-pressure pressure valve 13 a allocated to the pressure chamber 6 a are shown in FIG. 1.

External cooling 15 a, 15 b is provided on the outer circumference of the housing 2 in the region of the low pressure stage 5 and the high pressure stage 6.

For additional cooling of the piston compressor, the piston 4 has longitudinal boreholes 16 a, 16 b embodied as blind holes, which are connected to the drive pressure chambers 9 a, 9 b, whereby internal cooling of the piston compressor 1 is achieved through the pressurizing means driving the piston compressor 1.

In addition, the piston compressor 1 is provided with a displacement measuring system 17.

According to the invention, a compensating volume 20 a, 20 b with an adjustable dead volume is connected upstream of each pressure chamber 6 a, 6 b of the high pressure stage.

FIGS. 1 and 2 depict a longitudinal section of the compensating volume 20 a connected upstream of the pressure chamber 6 a. The compensating volume 20 b allocated to the pressure chamber 6 b has an identical structure.

The compensating volume 20 a is embodied as a compensating cylinder 21, which has a cylinder 23 that is longitudinally displaceable in a housing borehole 28 of a housing 22, whereby the adjustable dead volume formed by the compensating volume 20 a is embodied between the housing borehole 28 of the housing 22 and the cylinder 23, which is connected to the inlet of the pressure chamber 6 a of the high pressure stage 6 via a line 26, in particular to the connecting line connecting the pressure chamber 5 a of the low pressure stage 5 to the pressure chamber 6 a of the high pressure stage 6 downstream from the high pressure suction valve 12 a of the pressure chamber 6 a of the high pressure stage 6. The cylinder 23 is embodied as a stepped piston and has a first control surface 24 on a fore part arranged in the compensating volume 20 a, which control surface is acted upon by the intermediate pressure generated by the low pressure side and pending in the compensating volume 20 a. A second control surface 25 is embodied on an opposing fore part of the cylinder 23, and is acted upon by the inlet pressure of the low pressure stage. The second control surface 25 in this case is larger than the first control surface 24.

By correspondingly adjusting the cylinder 23 in the housing borehole 28, the compensating volume 20 a thus forms an adjustable dead volume for the pressure chamber 6 a of the high pressure stage 6.

A cooling device 27, which is formed for example by cooling fins arranged on the outer circumference of the housing 22, is arranged on the housing 22 in the region of the compensating volume 20 a.

In the depicted position with minimum inlet pressure of the piston compressor 1, the compensating volume 20 a has the maximum dead volume with the cylinder 23 deflected upwards in FIG. 2. With an increasing pending inlet pressure of the low pressure stage 5 on the second control surface 25 of the cylinder 23 that is embodied as a stepped piston, the cylinder 23 is acted upon downward in FIG. 2, whereby the compensating volume 20 a is acted upon in the direction of a minimum dead volume with maximum inlet pressure of the piston compressor 1.

When the piston compressor 1 is in operation, after the intake stroke in the compression stroke gaseous medium is conducted from the pressure chamber 5 a of the low pressure stage 5 via the pressure valve 11 a and the suction valve 13 a to the pressure chamber 6 a of the high pressure stage 6, which is in the intake cycle. By connecting the compensating volume 20 a to the connecting line leading from the low pressure stage 5 to the high pressure stage 6 downstream from the high pressure suction valve 13 a of the high pressure stage 6, compressed medium is also conducted from the low pressure stage 5 at the intermediate pressure to the compensating volume 20 a and thus to the adjusted dead volume and cooled via the cooling device 27. During the next intake stroke of the high pressure stage 6, whereby medium is suctioned from the compensating volume 20 a to the pressure chamber 6 a of the high pressure stage 6, the gaseous medium relaxes adiabatically from the compensating volume 20 a forming the dead volume and cools down in the process to below the intake temperature.

Because of the compensating volume 20 a controlled as a function of the inlet pressure, it is possible to change the intake volume of the high pressure stage 6 and therefore operate the compressor with different inlet pressures, whereby, due to the additional cooling of the medium by means of the compensating volume 20 a and in particular the cooling device 27, the temperature of the compressor can be reduced, in particular after the low pressure stage 5 with decreasing inlet pressure, whereby the stage pressure ratio and thus the thermal load of the high pressure stage 6 increases. 

1-15. (canceled)
 16. A compressor, in particular a piston compressor, for compressing a gaseous medium, having a low pressure stage for compressing the medium from an inlet pressure to an intermediate pressure, and having a high pressure stage for compressing the medium from the intermediate pressure to a high pressure, wherein a compensating volume with an adjustable dead volume is connected upstream of the high pressure stage.
 17. The compressor according to claim 16, wherein the dead volume formed by the compensating volume is adjustable as a function of the inlet pressure.
 18. The compressor according to claim 17, wherein the compensating volume is set at a minimum dead volume with maximum inlet pressure and with decreasing inlet pressure is adjustable in a direction of a maximum dead volume.
 19. The compressor according to claim 16, wherein the compensating volume is embodied as a compensating cylinder featuring a cylinder that is displaceable in a housing.
 20. The compressor according to claim 19, wherein the cylinder is provided with a first control surface as a stepped piston, which is arranged in the compensating volume and is acted upon by the intermediate pressure, and features a second control surface on an upper end which is acted upon by the inlet pressure.
 21. The compressor according to claim 16, wherein the compensating volume is provided with a cooling device.
 22. The compressor according to claim 21, wherein the cooling device is formed by cooling fins arranged on a housing of the compensating volume.
 23. The compressor according to claim 16, wherein the compressor features a piston that is longitudinally displaceable in a housing and which is driveable hydraulically.
 24. The compressor according to claim 16, wherein the low pressure stage has a first pressure chamber and a second pressure chamber.
 25. The compressor according to claim 16, wherein the high pressure stage has a first pressure chamber and a second pressure chamber.
 26. The compressor according to claim 16, wherein external cooling is provided on a housing of the compressor.
 27. The compressor according to claim 23, wherein internal cooling is provided on the piston.
 28. The compressor according to claim 23, wherein the piston is provided with at least one longitudinal borehole which is connected to a drive pressure chamber.
 29. The compressor according to claim 25, wherein a compensating volume is allocated to each pressure chamber of the high pressure stage.
 30. Use of a compressor according to claim 16 for compressing hydrogen, in particular in a hydrogen filling station.
 31. A compressor, comprising: a low pressure stage; a high pressure stage coupled to the low pressure stage; a piston moveably disposed within the low pressure stage and the high pressure stage; and a cylinder defining an adjustable gas volume coupled to the high pressure stage, wherein the gas volume of the cylinder is providable to the high pressure stage.
 32. The compressor according to claim 31, wherein the gas volume is adjustable by an inlet pressure to the low pressure stage.
 33. The compressor according to claim 32, wherein when the inlet pressure is at a minimum the gas volume is at a maximum and wherein when the inlet pressure is at a maximum the gas volume is at a minimum.
 34. A method of compressing a gas, comprising the steps of: compressing the gas in a low pressure stage of a compressor; providing a portion of the compressed gas from the low pressure stage to a cylinder; and providing a remaining portion of the compressed gas from the low pressure stage and the portion of the compressed gas from the cylinder to the high pressure stage.
 35. The method according to claim 34, further comprising the step of adjusting a gas volume of the cylinder by an inlet pressure to the low pressure stage. 